[ns] Hello,

["Jim Hawker" <jhawker@inari.com>]

Hello,

I am currently involved in evaluating network simulation tools that
could be used to model networks of devices over power lines such as
those in a home or office.  We are currently producing a device that
enables network nodes to communicate over power lines at rates on the
order of 1 to 2 Mbits/sec.  It uses a protocol that has been described
as "Datagram Sensing Multiple Access" using a "Centralized
Token-Passing" scheme.  It contains features of 802.2, 802.3, 802.5,
ATM, 802.11, and CEBus standards.  The physical layer utilizes multiple
RF regions or channels to simultaneously transmit packets from the node
that has the token to any other set of nodes.  Each RF channel can be
described as having time-varying characteristics that can affect the
delay, attenuation, and phase of bits transmitted through them.  In
addition, intersymbol interference effects can also be present.  The RF
channels can also be affected by broadband interference sources that
essentially produce time-correlated bit errors from channel to channel.

Because the time-varying nature of each channel affects each packet
stream differently I have among many others, the following
requirements:
       - The need to be able to model multiple channels simultaneously
transmitting packets between one node and any other node over the same
link.
       - The need to be able to model time-correlation effects between
channels in addition to the unique aspects of each time varying
channel.
       - The need to be able model the ability to modify the
transmission data rate and/or modulation scheme in response to changing
channel conditions.

After looking over the ns Notes and Documentation, the Marc Greis
tutorial, and downloading and running some of the examples in the
tutorial (ns-allinone-2.1b6) I still haven't decided whether ns could
model the multichannel nature of our system or not.  I believe that I
could specify error and channel models with ns that could be
time-varying in nature.  And ns provides the ability to create a new
MAC.  But I'm not seeing how I model simultaneous transmission of
multiple packet streams over the same link between any two nodes.  This
is sort of similar to ATM with virtual channels.  Anyone have any ideas
or done any work in ns like this before?

Also, since the manual page for ns on the web page is out of date, how
can I find out all of the possible ns commands and their options so I
can get a better idea of all of its capabilities?

Furthermore, is the node configuration API described in the Marc Greis
tutorial on page 3 only used for configuring wireless nodes?  If so, how
do I determine the scope or set of objects that any particular ns
command applies to?

Jim Hawker